In this work, dielec. spectroscopy was used to monitor two CHO perfusion culture expts. (B14 and B16). The capacitance of the cell suspension was recorded every 20 min over an excitation frequency range of 0.2 MHz to 10.0 MHz. A phase plot of the capacitance at a low excitation frequency vs. the value at a higher frequency proved to be an accurate indicator of the major transition points of the culture, i.e., max. cell viability, end of lactate consumption, point of zero viability. For both expts., the capacitance signal correlated very well (R2 >0.98) with viable cell no. up to concns. of 1 * 107 cells/mL. Visual observation of the capacitance spectra indicated that changes in the capacitance relative to frequency were related to the cellular morphol. A multivariate model was developed using off-line data that could predict the median cell diam. within a single expt. (B14) with an error of 0.34 mm (2%). Upon extension to a subsequent expt. (B16), the predicted error was 1.18 mm (9%). [on SciFinder (R)]